Field of the Invention
The present invention relates to a process for preparing polyether carbonate polyols, to the polyether carbonate polyols obtainable by this process and to the processing thereof for production of flexible polyurethane foams.
Description of Related Art
The preparation of polyether carbonate polyols by catalytic reaction of alkylene oxides (epoxides) and carbon dioxide in the presence of H-functional starter substances (“starters”) has been the subject of intensive study for more than 40 years (e.g. Inoue et al., Copolymerization of Carbon Dioxide and Epoxide with Organometallic Compounds; Die Makromolekulare Chemie 130, 210-220, 1969). This reaction is shown in schematic form in scheme (I), where R is an organic radical such as alkyl, alkylaryl or aryl, each of which may also contain heteroatoms, for example O, S, Si, etc., and where e, f and g are each integers, and where the product shown here in scheme (I) for the polyether carbonate polyol should merely be understood in such a way that blocks having the structure shown may in principle be present in the polyether carbonate polyol obtained, but the sequence, number and length of the blocks and the OH functionality of the starter may vary, and it is not restricted to the polyether carbonate polyol shown in scheme (I). This reaction (see scheme (I)) is environmentally very advantageous, since this reaction constitutes the conversion of a greenhouse gas such as CO2 to a polymer. A further product, actually a by-product, formed here is the cyclic carbonate shown in scheme (I) (for example, when R=CH3, propylene carbonate).

WO-A 2004/111107 discloses a process for preparing polyether polyols having terminal ethylene oxide chains with DMC catalysis, in which catalyst activation with propylene oxide is followed by metered addition of a mixture of propylene oxide and ethylene oxide with a constantly rising proportion of ethylene oxide (“ramping”), then depletion of the residual monomer and finally addition of pure ethylene oxide.
WO-A 2001/044347 discloses a process for DMC-catalyzed preparation of polyether polyols, in which at least two different epoxides are metered in together, with alteration of the ratio of the epoxides to one another in the mixture during the common metered addition.
WO-A 2008/058913 discloses a process for producing flexible polyurethane foams using polyether carbonate polyols prepared by means of DMC catalysis, wherein the polyether carbonate polyols preferably have a block of pure alkylene oxide units, especially pure propylene oxide units, at the chain end.
European patent application No. 11168433.8 discloses a process for DMC-catalyzed preparation of polyether carbonate polyols having a mixed block composed of at least two different alkylene oxides in a molar ratio of 15/85 to 60/40, and flexible polyurethane foams obtainable therefrom.
The polyether carbonate polyols known from the prior art have the disadvantage that, in the event of a (partial) exchange of a polyether polyol for a polyether carbonate polyol in a polyol formulation, the further constituents of the polyol formulation (additives) have to be adjusted in terms of type and/or amount for the processing to give flexible polyurethane foams, in order to achieve impeccable processibility. This is observed especially in the case of processing of the polyether carbonate polyols to give flexible polyurethane foams of the cold foam type (also referred to as high resilience or HR foam). However, it is desirable to be able to replace the polyether polyol at least partly with a polyether carbonate polyol while retaining the good processibility without having to adjust the further constituents of the polyol formulation (additives) in terms of type and/or amount.